Re: [CAD_CAM_EDM_DRO] Phase Converter

With all the variations in load, a static phase converter (capacitors) is
not a good solution. VFDs are for the motor only, not mag-starters or
varying loads, so that's out of the question. Sounds like you need a rotary
phase converter. Simplest is to just get a big 3-phase motor and either
pull-start it or put a 1-phase starter motor on it.

I'd like to upgrade my 2HP RF-31 to a VFD and an inverter duty motor. That
would be neat for soft starts as well as speed control and estop via
computer. Maybe someday ;-)

Paul R. Hvidston, N6MGN
ACKSYS Engineering
Upland, CA
p.hvidston@...

----- Original Message -----
From: <dp@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, March 26, 2002 10:07 AM
Subject: Re: [CAD_CAM_EDM_DRO] Phase Converter


> From: "Tim Goldstein" <timg@...>
> Date: Mon, 25 Mar 2002 15:42:36 -0700
>
> I have built a phase converter (it worked just fine) and then I bought
a
> VFD. I am much happier with the VFD than with the phase converter. Not
only
> does the VFD handle the phase conversion, but it lets me ramp up and
ramp
> down the mill so that when it starts there is no huge power draw and
when I
> shut it down it comes to a stop in about 1/4 of the time that it did
with
> the phase converter.
>
> If you are determined to build a phase converter there are about 4
links in
> the list off the FAQ page.
>
> Tim
>
> There styles of machine where a VFD is not an optimal solution. One
> with several motors is one where you may be better off with a
> converter. The other (at a minimum you will have to rewire) is one
> with a magnetic starter. To save some stress on their output
> transistors, the VFD's I have, ramp the motor up slowly. They don't
> like having a motor just cut in, and in the case of magnetic starters,
> you have to put the converter after the starter, and use its controls
> to start and stop the motor. If you just plug your machine into a
> VFD, without providing power for the starter relay, it won't have any
> voltage to engage, with the VFD set for "stop".
>
> My buddy has your basic huge Van Norman universal mill. We are just
> getting it running. I am loaning him a VFD so we can get some work out
> of it asap... Our first attempts to use it were less than an
> unqualified success.
>
> It has a 3hp spindle motor, with separate 2hp feed and (less than 1hp)
> coolant motors. It also has a magnetic starter for each of these. If
> you have the VFD running, and hit the spindle start button, it can
> overcurrent trip the VFD. If you try to use the VFD's controls,
> without re-wiring things, the start relay has no juice to engage
> before you tell the VFD to run.
>
> For now (we are just getting it back on-line) we will just wire
> straight from VFD to the spindle motor, and not try to power the feed
> or coolant motors. The switch box on the side is a pretty tangled
> mess, with 3 separate starter's, a big rotary switch to select what
> you want active (spindle, spindle and feed, spindle and coolant, all
> three...) so we aren't going to tackle it right now...
>
> -dp-